Saturday, June 09, 2012

Attack of the Tent Worms

Sounds like a good title for a B-horror movie doesn't it? A more common name for tent worms, is tent caterpillars. Each year, the Tent Caterpillar Moth (Malacosoma californicum) lays eggs on the stem of a deciduous tree. Favourite ones include aspens, cottonwoods, fruit trees, and in our area, alders. The eggs mature, but remain dormant until the following spring when tree leaves are at their prime.

After hatching, the tiny caterpillars build a tent they can use for protection and warmth in colder weather. When conditions are right, they wander off and begin eating their host tree. One tent worth of caterpillars can strip a full grown tree of about 20% of its leaves during the six weeks that the little furry critters feast. Then they form a cocoon to transform into a moth, starting the process all over.

Every 5-10 years for some unknown reason there is a population explosion. Tent caterpillars multiply in horrific numbers, denuding trees, getting under foot, and leaving a trail of poop pellets everywhere. And this is the year for Vancouver Island and the Sunshine Coast.

In the next few weeks we'll be inundated and our trees turned into a bare shadow of their former selves. Fortunately, a healthy tree can survive the onslaught and regrow the leaves needed for photosynthesis by mid-summer.

How are the caterpillars doing in your area? -- Margy


  1. How horrible! We don't have these, but the peskie cabbage white caterpillars eat my brassicas! xxx

  2. Yes, they get into everything. including my camera bag today! Thus one dead tent caterpillar.

  3. Fran - Sorry to hear that. We have some small blue butterfiles (or moths) hanging around the garden. Not sure what they are after, but they are very interested.

    Paul - Sorry to hear that. I saw a video on YouTube that had them crawling up the wall of a house in a huge mass. I definitely wouldn't like that.


  4. Ew, did not realized they are these nasty critters. Our yard was full of these crawling around.

  5. Stephanie - I was out again on Saturday and found trees almost completely stripped of their leaves. Hope what they say is true, that a health tree can rebound once the caterpillars go into the cocoon stage. - Margy